The proposed experiments have two goals: 1) to develop a horseradish peroxidase (HRP) histochemical method which does not involve enzymatic damage to the cells under study and 2) to refine the use of labelled nucleosides in trans-synaptic neuroanatomical experiments. The first group of studies will make use of HRP which has been chemically fragmented such that it retains less than 20% of its original enzymatic activity but essentially normal antigenicity. Antibodies will be used to detect the "apo" - HRP. The value of the new technique will be analyzed by measuring cell uptake and transport of the fragmented enzyme in a variety of brain areas. The material will be ejected by pressure for tract tracing experiments and by iontophoresis for cell labelling experiments. The second set of experiments will use microdissection of discrete hippocampal layers and liquid scintillation counting to test for the amount of trans-synaptic transport of a variety of labelled aminoacids and nucleosides. The afferents of the hippocampus terminate in dendritic layers which are quite distinct from the cell body layers. Consequently, by measuring the amount of label in the zones of termination (which includes both pre- and post-synaptic elements) and comparing it with that in the cell body layer (which is purely post-synaptic), it is possible to arrive at a quantitative measure of trans-synaptic transport. Using these procedures we have found that adenosine crosses at least one synapse in hippocampus much more readily than a test amino acid. In future work we will: 1) use other test systems to see if adenosine shows this property universally, 2) use other amino acids and nucleosides to establish if the effect is truly unique to adenosine and 3) begin autoradiographic experiments to establish if the transported material will be retained through this procedure. BIBLIOGRAPHIC REFERENCES: Lynch, G., Smith, R., Browning M.D., and S. Deadwyler. Evidence for bidirectional dendritic transport of horseradish peroxidase. In: G. Kreutzberg (ed.) Advances in Neurology Vol. 12, New York: Raven Press, 1975, pp. 297-313.